Tachometer.



E. B. BROWN.

TACHOMETER.

APPLICATION FILED IAN.18.1912.

Patented July 29, 1913.

,.HH.......M.N..wwmIk NVENTOFS', ada/m1,(

WlT/vEssEs; MW 1/ @JMW u )UNTTED STATES PATENT GFECE.

EDWARD BYAM BROWN, OF MELBOURNE, VICTORIA, AUSTRALIA.

TACHOMETER.

Specification of Letters Patent. Patented July 29, 1913.

Application filed January 18, 1912.k Serial No. 671,779.

speeds of rotation being applicable eitherV for the measurement of speeds of rotation only or when such speeds of rotation are- 'transferred into linear speeds as in speedometers for vehicles and the like.

This invention relates to'tachometers containing permanent magnets and embodies the `use of. the magnetic effect of electric currents inducedy in conductors moving in a permanent magnetic field. e

Hitherto tachometersor speed indicators embodying the use of the magnetic effect of electric `currents induced in conductors moving in a permanent magnetic field have comprised for the` most part those consisting of a volt meter used in combination with a dynamo with permanent magnets, the armature of which is' caused to rotate at a speed which is Va multiple of that required to be measured. In this volt meter the moving element whichindicates vthe -speedis operated against the tension of `a controlling spring. Other instruments have also been constructed in which use is made of the torque due to eddy currents induced in a plate of metalpivoted over permanent rotating magnets, the movement of the said plate being also against the tension of a controlling spring. These instruments have been more orless unreliablein use,.owing to the l indicating Amechanism being controlled by a spring which is subject to variations of temperature and other conditions, and to the permanent magnets being subject to change and variation due to vibration and other causes. v y

The object of this invention isA to provide a tachometer or speed indicator which is not controlled by any spring device and in which theaccuracy is not dependent upon the strength of the permanent magnet.

ln an instrument constructed according to my invention the indicator automatically adapts itself to any alterations or variations in the said magnet, and there are no moving contacts in the electrical circuit (as in the dynamo and volt-meter type) so that there are no possibilities of error due to the variable resistance of moving contacts (such as the commutat-ors and brushes) while the permanent magnet is not rotating (as in the eddy 4current type). Furthermore the sensitiveness of the instrument may be adjusted by altering thev magnetic field so that the scale may be made to read over a wide range of speeds. I accomplish this object by providing an instrument which comprises a permanent magnet between the poles of which is set a rotating armature consisting of an iron core provided with projecting conductors forming an insulatedcontinuous wind- 1ng preferably in the form of a squirrel cage l winding by which a secondary magnetic field is induced. This armature is mounted inv suitable' bearings and is causedtov rotate by being connected to the moving body, the speed of which -is to be recorded. Within the said projecting conductors is mounted a llight shaft Aor spindle' carrying a plate of soft iron the said shaftfor spindle being colinear with the axis of thearmature This plate of soft iron when in its normal position sets itself inthe direction of the 'magnetic field between the poles 'of the permanentY` magnetand 'when the A'armature is rotated the said. plate adapt'sitself to the resultant magnetic el ddu`e to the pei-ma'-Y nent magnet and the currents in the revolving conductors. An'.- indicating. needle is attached to this shaft or spindle which indicates the direction of the said resultant magnetic eld upon a graduated scaleand consequently the speed of rotation.

The invention will now be more fully described aided by a reference lto the accompanying sheets of drawings in which Figure l isav full elevation of'an instrument constructed according to my invention. Fig. 2 is a plan, and Fig. 3 a vertical section of the same on the line a-a Fig. 2, the permanent magnet being shown ypartly by dotted lines.` Fig. 4 is a part/side elevation and part'vertical section von the line b-b Fig'. 2, the means of connection to the rotating body being shown as bevel gearing. Fig. 5 is a horizontal section on the line c-c, Fig. 3. Fig. 6 is a detail perspective view of the rotating armature with its proj ecting conductors. Fig. 7 is a View similar to Fig. 6 showing a modified form of armature.

In constructing a tachometer or speed in dicator according.' to my invention I provide a metal casing 1 within which are supported two iron pole pieces 2 on which is adjustably secured a permanent magnet 3. The ends ot the said magnet 3 are adapted. to project above the pole pieces 2 to any Adesired extent, to enable the strength of the magnetic field above the pole pieces 2 to be varied' and for this purpose the magnet' 3 is fitted within grooves 4. formednin the casing 1, and the'pole pieces 2. "The magnet 3 is-adapted to slide within these grooves 4e and is held in place by clamps 5 or other convenient means.l The magnet 3 may be set' at an incline as shown in Fig.` 1 so as tofclea'rthe connecting rotating shaft, or it may be bent or curved for thesame purpose, or it mav be straight, as vshownin Fig. 4, when bevel connecting' gearing is used. w

Between the pole pieces 2 is mounted an iron armature comprising a core 6' support' ed upon a spindle 7 working in (preferably)"i ball'bearings 8- within the casing 1. This spindle 7 is provided with means for connection to the` rotating body the speed of which itis desired to measure, such as a flexibleV shaft 'as shown in. Fig. 1, or bevel gearing as'shown in Fig. 4.

j The-'rotating' armature isprovided `with anyV formV of insulated continuous armature winding by which' ai secondary-magnetic field isinduced vfrom the primary magnetic field. "For this purpose the larmature is provided with laterally projecting insulated conductors9 (preferably of-c'opper) which are accommodated within lslots' in thepe! riphery offthe core 6 beinginsulated there?v from by"red fiber 'or otherl insulationV 10. The 'extremities of these conductors are connected by a ring 1 1 and thelower ex-l tremities by a ring. 13. The armature is thus similar to the wellknownsquirrel cage armature winding-used in induction motors.v TheA projecting conductors 9' may be made parallel Awith the longitudinal axis or may be bent inward, as shown in the drawings, for the purpose of increasing the magnetic effect of the currents.

Within the projecting conductors 9 of the armature, but not connected therewith is a stationary cylinder 14 arranged vertically and connected to the top plate 15 of the instrument. Within this cylinder 14 is mounted a vertical Spindle 16, -theaXis of'which, is colinear with the axis of the armature,l being mounted, in the adjustable bearings 17 which have a minimum offriction being preferably of jewels or hardened steel cups so that the indicator needle may easily move to and fro. This light spindle 16 is furnished at its lower end with a soft iron plate 18 and at its upper end with an indicating needle 19. For the purpose of damping the vibrations of the indicating needle 19, it is provided with a rearwardly projecting vane. 20: whichworks or operates with small clearance in an inclosure or box 21. formed on the top plate 15 of the instrument. Means are provided for balancing the moving element comprising the. indicator needle 19, the vane 20, the shaft 16 and soft iron plate 18 which consists of .wires 24 or the like upon the said needle as shown in Fig. 2 so that the instrument will indicate correctly in any position.

The top plate 15 of the instrument is provided with a transparent cover, having air and water tight joints So that the indicating of the instrument will not be affected by weather conditions. A graduated scale 22 is attached to the top plate 15 of the-instrument immediately underneath the point of the needle. 19,='so that the speed of the rotating armaturei'and "that of the rotating body connected thereto'vmay be indicated.

Then the armature rotates, as 'actuated' 'by the body the speed ofwhich it is desired'.

to register, a change is producedin thediv` 1 rect-ion of theV magnetic field between 'the' poles ofJ'the permanent l'r'nagnetffby,the cross magnetic field produced-'bythe cur,`

`rents which i'ow in the-conductors 9. The' resultant magnetic ,ti'e'ld'f influenced-the soft -iron plate 18A attached thelight?"Sha-ftif/(irN spindle 16, thus causingqtheneedle19- Qto" indicate. upon,` the scale .22thedirection*cil the same,VV and lconsequently vthe Yspeed tation. 'f

. duce-the magneticv field throughflthezarinatfure and' produce thefmagntictieldjacross ths-pace withinftliel ndueto'rgig of Vthe"jrotatin'g'"'armatureg' i A 'g that any Vchangein the" strength Qfth will;

. marient mag-netje' iwiuf-'noeafieath:direc: tion. of the resultant'tieldj"produced* since lbeth the initial component-'ofithefeldpreseen 5' ofrpeentin :th'atspace when tlie"armati1re"was"at rest and likewise the deflecting cbmp'onentcaused'by the currents'induced by' the 'rota tion of the armature' arelalectedfto-the'same extent.

The sensitivenessV of' the instrument 1can be adjusted over a wide rangefby sliding the magnet 3 up or v"down in fthe' 'grooves'4 inthe casing 1 and 'pole pieCeS'ZlfThiST-adjustment of thei'magnets' may betu'sed for adapting the same instrument to `suit 'a dif-v ferent range of speeds. Whenfused" as a speedometer for vehicles the same instru# ment andv connectingfgea-r may beadapted to indicate correct readings 'with vehicles having wheels of `varying sizes.

In instruments where'speeds of rotation in both directions are required the arrangement of bevel gears as shown in Fig. 4t may be employed, when either end of the shaft 23 may be connected to the rotating body according to the direction of rotation.

The instrument may be operated in the reverse direction without damage and advantage maybe taken of this fact by so arranging the parts that the indicator needle is in the center of the graduated scale when the armature is at rest. The center of the scale is then zero and the scale is graduated upon either side for direct and reverse speeds of rotation.

I claim 1. A tachometer comprising a permanent magnet between the poles of which is mounted a rotatable armature core provided with projecting insulated conducto-rs comprising a continuous winding, by which a secondary magnetic field is induced, a shaft and a piece of soft iron mounted on said shaft within the said secondary field, said shaft having an indicating needle, substantially as described.

2. In tachometers comprising a permanent. magnet between the poles of which is mounted a rotatable armature core having insulated conductors in the form of a squirrel cage winding attached thereto, by which a secondary magnetic field is induced, a shaft and a piece of soft iro-n mounted on said shaft within the said secondary field, said shaft having an indicating needle sub stantially as described.

3. In tachometers comprising a permanent magnet between the poles of which is mounted a rotatable armature core having insulated conductors connected at their eX- tremities to rings and being bent inward and then again bent parallel to the axis, by which a secondary magnetic field is induced, a shaft and a piece of soft iron mounted on said shaft within the said secondary field, said shaft having an indicating needle substantially as described.

4. In tachometers comprising a rotatable armature core having conductors fo-rming an insulated continuous winding, an adjustable permanent magnet between the poles of which said core is mounted, by which a secondary magnetic field 1s induced, means for holding said magnet in its adjusted position relatively to the co-nducto-rs of said rotatable armature core, a shaft and a piece of soft iron mounted on said shaft within said secondary field, said shaft having an indicating needle substantially as described.

5. In tachometers comprising a permanent magnet between the poles of which is mounted a rotatable armature core provided with insulated continuous winding by which a secondary magnetic field is induced, a shaft and a piece of soft iron mounted on said shaft within the said secondary field,v

said shaft having an indicating needle, and means for damping the movement of the needle, substantially as described.

6. In tachometers comprising a permanent magnet between the poles of which is mounted a rotatable armature core provided with insulated continuous winding by which a secondary magnetic field is induced, a shaft and a piece of soft iron mounted on said shaft within the said secondary field, said shaft having an indicating needle, and means for damping the movement of the needle, comprising a vane attached to the tail of the said needle and a box within which said vane moves with small clearance, substantially as described.

7. A tachometer comprising a casing 1, pole pieces 2, a permanent magnet 3, a rotatable armature core 6 having conductors 9 with their extremities connected by rings 11 and 13, a spindle 16 mounted in bearings 17 having a soft iron plate 18 and an indicating needle 19, a damping vane 20 working in a box 21 and a graduated scale 22, substantially as described, and as sho-wn in the drawings.

In testimony, that I claim the foregoing as my invention, I have signed my name in presence of two subscribing witnesses.

EDWARD BYAM BROW'N.

Witnesses:

CLEMENT A. HACK, CYRIL WRIGHT.

Copies of this patent may be obtained for five cents each, by addressing the Commissioner of Patents.

Washington, D. C. 

